Different kinds of sensors and detector structures are known for detecting neutrons. Neutrons as such cannot be detected directly but via interactions with neutron reactive materials producing radiation reaction products responsive to interactions with the interacting neutrons. The neutron reactive material converts the invisible radiation to detectable signals. If the radiation consists of charged particles, such as alphas, electrons or positrons, the electromagnetic interaction create charges which can be collected and detected.
All detectors use the fact that the radiation interacts with matter, mostly via ionization. One of the detectors used for detecting neutrons is a Helium-3 detector tube, where Helium-3 gas is used as a converter gas for capturing neutrons and “converting” captured neutrons into charged particles to be detected. The neutron is “converted” through the nuclear reactionn+3He→3H+1H+0.764 MeVinto charged particles tritium (T, 3H) and protium (p, 1H), which can be detected e.g. by creating a charge cloud in the stopping gas of a proportional counter or a Geiger-Müller tube, for example.
There is however some problems related to the known solutions. Even though Helium-3 gas has a high absorption cross section for thermal neutron beams and is widely used, it is very rare on Earth and thus the detectors based on the use of Helium-3 are quite expensive. In addition, since most of the neutron sources or reactions are accompanied by a gamma or X-ray background and because the neutral gamma or X-ray radiation interacts with semiconductor matter of the detectors, the gamma or X-ray background will disturb the accurate measuring, which is an undesired effect.